Ketamine inhibits nitric oxide synthase in lipopolysaccharide-treated rat alveolar macrophages

Purpose: To evaluate the effects of ketamine on the activity and protein expression of inducible nitric oxide synthase (iNOS) induced by lipopolysaccharide (LPS) in rat alveolar macrophages. Methods: Pulmonary alveolar macrophages isolated from Wistar-Kyoto rats were used. After incubation of macrophages with ketamine (1, 10, or 100 mu M) and LPS (1 mu g.ml(-1)) for 24 hr, the cell-free medium was removed for measuring the nitrite and tumour necrosis factor-alpha (TNF-alpha) levels by Griess reaction and ELISA kit, respectively. The harvested macrophages were also used to determine the activity of iNOS by using the conversion of [H-3]-L-arginine to [H-3]-L-citruliine method. In addition, the protein expression of iNOS was detected by Western blot analysis. Results: In rat alveolar macrophages, (1) ketamine (1 to 100 mu M) caused a dose-dependent suppression of the production of nitrite and TNF-alpha induced by LPS and (ii) ketamine (100 mu M) inhibited the activity (46.5 +/- 4.8%, P < 0.05) and protein expression (35 +/- 11%, P < 0.05) of iNOS in response to LPS. Conclusion: These results show that ketamine inhibits the activity and expression of iNOS in LPS-activated alveolar macrophages, which may be associated with the reduction of the release of TNF-alpha following LPS treatment.